Nontypable Haemophilus influenzae (NTHi) are primarily noninvasive human respiratory tract pathogens. NTHi can reside in the respiratory tract as a commensal organism or give rise to local infections, including otitis media, bronchitis, sinusitis, and rarely, pneumonia (1, 12). Several potential adherence factors have been described for NTHi adherence to human cells, including four classes of fimbriae/pili and two high molecular weight proteins with similarity to the filamentous hemagglutinin of Bordetella pertussis. (16).
One class of NTHi pili/fimbriae has been widely studied. The long thick pili (LKP) family are hemagglutination positive and mediate attachment to human mucosal cells (2). LKP pili are expressed by both NTHi and H. influenzae type b (Hib). They have also been shown to be vaccine candidates for NTHi otitis media in the chinchilla model, conferring protection against challenge with NTHi strains bearing the homologous pili serotype (8). The LKP family has been divided into 14 different strain specific types based on reactivity to polyclonal antisera raised against the purified pili. Little cross reactivity among pilus serotypes has been observed (2). Hemagglutination of human erythrocytes is accomplished via binding to the AnWj blood group antigen while binding to epithelial cells involves a sialic acid containing lactosylceramide receptor (18). Operons LKP pilin structural genes have been cloned and sequenced by several groups (4, 5, 7, 19), but only the genes responsible for pili serotypes 1 and 4 have been identified.